Processing of the NF-KB2 p100 precursor protein to generate p52, which is tightly controlled, is important for proper regulation of NF-KB function in cell growth and survival. Aberrantly persistent processing of p100 causes abnormal lymphocyte proliferation and transformation. Accordingly, enhanced p100 processing is associated with various human malignancies, particulary lymphomas/leukemia. Tax, an oncoprotein encoded by human T-cell leukemia virus type I (HTLV- I), the etiological agent of adult T-cell leukemia (ATL), is the first pathogenic inducer of p100 processing and responsible for overproduction of p52 in leukemic T cells transformed by HTLV-I. Thus, the long-term objective of this research project is to use HTLV-l/Tax as a model system to elucidate the molecular mechanism by which p100 processing is regulated and involved in tumorigenesis, for preventive and therapeutic purposes. The central hypothesis of this investigation is that deregulated processing of p100 contributes to tumorigenesis. The rationale for the proposed research is that, once the mechanisms by which p100 processing is deregulated under pathogenic conditions have been determined, this information can be used to specifically block p100 processing to prevent and treat lymphomas/leukemia including ATL, and other diseases associated with p100 processing. The objective of this proposal is to investigate the mechanisms of HTLV-l/Tax-induced p100 processing and its involvement in tumorigenesis. The specific aims of this proposal are: (1) to characterize cellular factors regulating Tax-induced processing of p100;(2) to define the p-TrCP (an E3 ubiquitin ligase)-independent mechanism involved in pathogenic, but not physiological, processing of p100;(3) to determine the mechanism by which p100 processing regulates HTLV-l/Tax-induced cell transformation and tumorigenesis. The completion of the proposed studies may lead to new therapeutic strategies for p100 processing-associated human diseases.